Various diameter hole saws that utilize a single-pilot, drill--containing mandrel--the mandrel being switched from one size to another size hole saw--are well known in the art.
For example, a typical hole saw consists of a cylindrical saw that forms a heavy base end with a threaded axially aligned hole in the bore. A threaded mandrel is adapted to screw into the base of the hole saw from the outside or base end of the saw. The mandrel at its threaded end forms a hole to accept the shank of a drill, the opposite end of the mandrel forming a shank designed to be received by the chuck of a drill motor or the like. Intermediate the threaded end and the shank of the mandrel is a flange formed typically in a round or hex-nut shape for securing the mandrel in the base of the hole saw. A slotted screw on the flange secures the shank of the pilot drill positioned in the hole formed in the threaded end of the mandrel.
A right-hand thread is normally used to secure the mandrel and the hole saw. In use then, when the serrated end of the saw contacts the surface of the material to be sawn, a reactive force between the hole saw and the mandrel tightens the mandrel against the saw allowing it to cut. After the saw cuts the hole, the plug of material then must be removed from the interior of the hole saw. Slots are normally formed by the hole saw body so that the plug may be pried out of the saw, a tedious task at best.
Another well known hole saw utilizes a slightly different configuration. The single mandrel for the various diameter hole saws consists of a mandrel body having a first flanged base end and a second, smaller--diameter, threaded end--the mandrel further forming an axially aligned hole therethrough adapted to accept a drill bit. The shank of the drill bit has flats to accept a slotted screw retained in the mandrel flange to secure the drill in the mandrel. The shank end of the drill is used to secure the hole saw in a drill motor as heretofore described. The flange of the mandrel is stepped down in diameter, forming a circular shoulder at its base, the intermediate flange being formed with flats that conform to complimentary flats formed in the base of the hole saw. The drill-containing mandrel then is inserted through the open serrated end of the hole saw, the intermediate flange flats being aligned with the flats of the hole saw to prevent rotation of the mandrel with respect to the hole saw. A threaded nut then is slipped over the shank of the drill and tightened into the threaded end of the mandrel protruding through the base of the hole saw, thereby securing the hole saw between the mandrel and the nut.
Again, slight movement between the hole saw and the mandrel will easily loosen the nut when the cutting end of the hole saw contacts the surface to be cut.
To remove the plug of material from the interior of the hole saw, the hole saw must be removed from, for example, the power drill. The nut is then removed from the mandrel, followed by forcibly driving the mandrel and plug out of the open end of the hole saw.
As an alternative, holes formed in the circular side wall of the saw enable the plug of material to be pried or split out of the mandrel, as previously described.
Some state-of-the-art hole saws utilize a washer and spring arrangement internally of the hole saw to keep the saw round while cutting.
The prevent invention overcomes the obvious deficiencies of the foregoing prior art by providing a means to easily remove a plug of material from the interior of a hole saw. This is accomplished without utilizing knives or picks or complete dismantling of the apparatus of the hole saw.